Long term evolution (LTE) may denote the fourth generation (4G) communication technology. LTE has been developed for increasing a data transmission rate, for efficiently using radio resources such as allocated frequencies, for improving mobility, for reducing communication latency, for optimizing packet data transmission, and for guaranteeing a service quality level. Lately, LTE communication networks have been commercialized in various countries in Asia, North America, and Europe. The LTE communication network has been implemented over existing 3rd generation (3G) communication networks, for example, wideband code division multiple access (WCDMA) communication networks. Accordingly, the LTE communication network may co-exist with a WCDMA communication network. The LTE communication network, however, may be available only in certain areas. For example, the LTE communication network is only available for certain regions in South Korea. The LTE communication network has not been expanded to cover the entire country of South Korea.
The LTE communication network may include a plurality of LTE macrocells and LTE small cells. A LTE macrocell may provide a communication service in a comparatively wide area by a LTE macrocell base station. A LTE small cell may provide a LTE communication service in a comparatively small area by a LTE small cell base station. LTE small cells may include a LTE microcell, a LTE picocell, and a LTE femtocell. The LTE microcell may be used in a densely populated urban area. The LTE picocell may be for area even smaller than LTE microcells, such as a large office, a mall, or a train station. The LTE femtocell may provide a communication service in the smallest area compared to the LTE microcell and the LTE picocell. Such a LTE femtocell may be installed at a small office or home to provide a LTE communication service. Accordingly, LTE macrocells may overlap with a plurality of LTE small cells such as LTE microcells, LTE picocells, and LTE femtocells. Furthermore, the WCDMA communication network may include a plurality of WCDMA macrocells. A WCDMA macrocell may provide an associated communication service in a comparatively wide area by a WCDMA macrocell base station. As described above, the LTE communication network is built above the WCDMA communication network. Accordingly, LTE macrocells may overlap with WCDMA macrocells.
In a LTE communication network, the limited number of identification codes may be used for identifying each LTE base station. For example, about 504 physical cell identities (PCIs) may be used to identify LTE base stations in the LTE communication network. Since the number of PICs is limited, the PCIs may be required to be reused. In case of LTE macrocells, the reuse of PCIs may not cause a problem because a service area of each LTE macrocell is comparatively large and LTE macrocells are distributed over a comparatively wide area. In the case of LTE small cells, such as a LTE femtocell, the reuse of PCIs may cause a problem because a plurality of LTE small cell base stations may be installed in a comparatively small area. Accordingly; it may be difficult to identify each LTE small cell base station only with PCIs.
Due to such shortage in PCIs, user equipment may not be normally handed over from a LTE macrocell to a LTE small cell. For example, user equipment may frequently enter into a LTE femtocell from a LTE macrocell while the user equipment is receiving a LTE communication service from an associated LTE macrocell base station. In this case, the user equipment may not identify a LTE femtocell base station of the newly entered LTE femtocell. Accordingly, the user equipment cannot be handed over to the LTE femtocell base station. Such handover failure problem may lead frequency interference, service quality deterioration, power increment and cell capacity decrement in LTE macrocell base stations, and uplink coverage shrinkage in LTE femtocell base stations.